Simple Route to Metal cyclo-N₅^– Salt: High-Pressure Synthesis of CuN₅

A naked cyclo-N5– salt has yet to be recovered to ambient conditions, precluding its application as a high-energy density material for explosive or propulsion applications. Here, we suggest a simple route for the synthesis of a metal cyclo-N5– salt via compressing CuN6. Using first-principles calculations with structural search, we predict a CuN5 compound with a cyclo-N5– anion that is energetically favorite in the pressure range of 50–100 GPa....